1. Field of the Invention
The present invention relates, in general, to shock absorbing devices for steering columns and, more particularly, to a shock absorbing device for steering columns which has a simple construction and is easily produced, and is capable of absorbing a high impact.
2. Description of the Related Art
To absorb a collision impact which may be transferred to a driver through a steering column when a vehicle is involved in a collision, and to protect the driver from such a collision impact, a shock absorbing device is used with the steering column. An example of conventional shock absorbing devices for steering columns is referred to in Korean Patent Laid-open Publication No. 2000-10034.
Generally, the steering apparatus of an automotive vehicle comprises a manipulation mechanism through which a driver inputs a steering motion and the steering motion is transmitted to both a steering gear mechanism and a link mechanism. The steering gear mechanism reduces the rotation angle of a steering shaft of the manipulation mechanism, thus increasing a driver's steering force, and converts the direction of the steering motion. The link mechanism transits the motion of the steering gear mechanism to the front wheels while supporting the positional relation between the left and right wheels. The steering shaft of the manipulation mechanism is surrounded by a steering column, with a shock absorbing device provided on the steering column to protect the driver from a collision impact which may be transferred to the driver through the steering shaft and the steering wheel when the vehicle is involved in a collision.
The shock absorbing device allows both the steering shaft and the steering column to be deformed in response to a collision impact, thus absorbing the impact energy. Conventional shock absorbing devices for steering columns are typically classified into three types: mesh-type shock absorbing devices using steering columns having net structures capable of contracting in response to a collision impact, thereby absorbing impact energy, bellows-type shock absorbing devices using bellows tubes; and ball and sleeve-type shock absorbing devices using balls and sleeves.
The three above-mentioned types of conventional shock absorbing devices are configured to absorb a collision impact energy through contracting and buckling. In addition to the three types of conventional shock absorbing devices, another type of shock absorbing device having capsules provided outside a steering column and breaking in response to a collision impact, thus absorbing impact energy, has been proposed and used.
As shown in FIGS. 1 and 2, a conventional shock absorbing device with capsules is mounted to a vehicle body 140 using a bracket 120 as well as the capsules 123. The bracket 120 has a capsule locking slot 120a at each end thereof, while each of the capsules 123 made of aluminum has a longitudinal hole 123a. The shock absorbing device is mounted to the vehicle body 140 by engaging the capsules 123 in the slots 120a of the bracket 120 and locking the capsules 123 to the vehicle body 140 using locking bolts 124 which pass through the longitudinal holes 123a of the capsules 123. The capsules 123 are breakably assembled with the bracket 120 using plastic pins 160. The plastic pins 160 are broken in response to a collision impact, thus executing a shock absorbing function, in addition to the function of breakably assembling the capsules 123 with the bracket 120.
When a collision impact is transmitted upwards through a steering column 110, the upper jacket 111 of the steering column 110 moves downwards along the outside surface of the lower jacket 113. Thus, the steering column 110 contracts and buckles, thereby primarily absorbing impact energy. At this time, the bracket 120 which moves along with the upper bracket 111 in the same direction is quickly separated from the capsules 123 bolted to the vehicle body 140. Therefore, the plastic pins 160, which have breakably assembled the capsules 123 with the bracket 120, are broken, thus secondarily absorbing the impact energy and reducing injury to a driver due to the impact.
However, each of the capsules 123 must be configured to have a complex shape capable of undergoing an assembly process which has been typically executed through plastic injection molding to assemble the capsules 123 with the bracket 120, so that aluminum die-cast products have been preferably used as the capsules 123. However, due to the intrinsic properties of aluminum, the aluminum die-cast capsules 123 easily break during a process of assembling the capsules 123 with the vehicle body 140 or when the vehicle body 140 vibrates. Thus, the operational reliability of the shock absorbing device is reduced. Furthermore, a part of each of the aluminum die-cast capsules 123 must be post-processed after die-casting, thus increasing the manufacturing costs of the shock absorbing devices. When the plastic pins 160 are formed on the capsules 123 through plastic injection molding to breakably lock the capsules 123 to the bracket 120, the injection molding work conditions are remarkably changed according to operational reliability and stability of a molding machine. Thus, the separation load imposed on the plastic pins 160 to separate the bracket 120 from the capsules 123 is distributed in an excessively large range, so that the shock absorbing function of the plastic pins 160 is reduced. Furthermore, when a vehicle runs, the capsules 123 may become detached from the bracket 120 or fail to perform a designed shock absorbing function when an excessive impact is applied thereto. Furthermore, the capsules 123 have complex structures, thus increasing manufacturing costs and entailing complex assembly processes of the shock absorbing devices.